1. Field of the Invention
The present application relates generally to atomic layer deposition of dopant films, such as doped silicon oxide thin films.
2. Background
With the scale down of devices, deposition of dielectric films with good step coverage is desirable. Traditional ALD is a self-limiting process, whereby alternated pulses of reaction precursors saturate a substrate surface and leave no more than one monolayer of material per pulse. The deposition conditions and precursors are selected to ensure self-saturating reactions, such that an adsorbed layer in one pulse leaves a surface termination that is non-reactive with the additional gas phase reactants of the same pulse. A subsequent pulse of different reactants reacts with the previous termination to enable continued deposition. Thus each cycle of alternated pulses leaves no more than about one molecular layer of the desired material. The principles of ALD type processes have been presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, the disclosure of which is incorporated herein by reference.
Sequencing, which is a characteristic of an ALE process, can be performed either by valving the fluxes of the reactants or by using a moving substrate holder which exposes the substrates sequentially to fluxes of different reactants. Examples of ALE reactor constructions using rotating substrate holders are presented in U.S. Pat. No. 4,058,430 and Colter et al. MRS Symp. Proc. 222:157 (1991), see also FIGS. 25A and 25B. Advantages of a rotating substrate holder are a high sequencing speed, reliable operation and easy application to different types of reactants, including reactants which need high-temperature sources. A disadvantage of systems based on rotating substrate holders is a smaller flexibility to achieve the complex sequences needed in superlattices or multilayer structures. Also scaling up of systems with moving substrates is more difficult than for systems with static substrates.
As described herein, Atomic Layer Deposition (ALD) processes can be used to deposit doped silicon oxide, such as BSG and PSG. ALD provides good step coverage on three-dimensional structures.